001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.context.annotation;
018
019import java.lang.annotation.Annotation;
020
021import org.springframework.core.GenericTypeResolver;
022import org.springframework.core.annotation.AnnotationAttributes;
023import org.springframework.core.type.AnnotationMetadata;
024import org.springframework.lang.Nullable;
025import org.springframework.util.Assert;
026
027/**
028 * Convenient base class for {@link ImportSelector} implementations that select imports
029 * based on an {@link AdviceMode} value from an annotation (such as the {@code @Enable*}
030 * annotations).
031 *
032 * @author Chris Beams
033 * @since 3.1
034 * @param <A> annotation containing {@linkplain #getAdviceModeAttributeName() AdviceMode attribute}
035 */
036public abstract class AdviceModeImportSelector<A extends Annotation> implements ImportSelector {
037
038        /**
039         * The default advice mode attribute name.
040         */
041        public static final String DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME = "mode";
042
043
044        /**
045         * The name of the {@link AdviceMode} attribute for the annotation specified by the
046         * generic type {@code A}. The default is {@value #DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME},
047         * but subclasses may override in order to customize.
048         */
049        protected String getAdviceModeAttributeName() {
050                return DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME;
051        }
052
053        /**
054         * This implementation resolves the type of annotation from generic metadata and
055         * validates that (a) the annotation is in fact present on the importing
056         * {@code @Configuration} class and (b) that the given annotation has an
057         * {@linkplain #getAdviceModeAttributeName() advice mode attribute} of type
058         * {@link AdviceMode}.
059         * <p>The {@link #selectImports(AdviceMode)} method is then invoked, allowing the
060         * concrete implementation to choose imports in a safe and convenient fashion.
061         * @throws IllegalArgumentException if expected annotation {@code A} is not present
062         * on the importing {@code @Configuration} class or if {@link #selectImports(AdviceMode)}
063         * returns {@code null}
064         */
065        @Override
066        public final String[] selectImports(AnnotationMetadata importingClassMetadata) {
067                Class<?> annType = GenericTypeResolver.resolveTypeArgument(getClass(), AdviceModeImportSelector.class);
068                Assert.state(annType != null, "Unresolvable type argument for AdviceModeImportSelector");
069
070                AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
071                if (attributes == null) {
072                        throw new IllegalArgumentException(String.format(
073                                        "@%s is not present on importing class '%s' as expected",
074                                        annType.getSimpleName(), importingClassMetadata.getClassName()));
075                }
076
077                AdviceMode adviceMode = attributes.getEnum(getAdviceModeAttributeName());
078                String[] imports = selectImports(adviceMode);
079                if (imports == null) {
080                        throw new IllegalArgumentException("Unknown AdviceMode: " + adviceMode);
081                }
082                return imports;
083        }
084
085        /**
086         * Determine which classes should be imported based on the given {@code AdviceMode}.
087         * <p>Returning {@code null} from this method indicates that the {@code AdviceMode}
088         * could not be handled or was unknown and that an {@code IllegalArgumentException}
089         * should be thrown.
090         * @param adviceMode the value of the {@linkplain #getAdviceModeAttributeName()
091         * advice mode attribute} for the annotation specified via generics.
092         * @return array containing classes to import (empty array if none;
093         * {@code null} if the given {@code AdviceMode} is unknown)
094         */
095        @Nullable
096        protected abstract String[] selectImports(AdviceMode adviceMode);
097
098}